Organic el light-emitting device

ABSTRACT

An organic EL light-emitting device including: a light-emitting layer capable of generating light; a light-scattering structure capable of scattering the light; a first light-scattering layer containing first light-scattering particles having an average particle diameter of 0.1 μm to 2 μm and a first binder; and a concavo-convex structure in a streak array pattern, the light emitting layer, the light-scattering structure, the first light-scattering layer, and the concavo-convex structure being disposed in this order, wherein a mean free path L 1  of light scattering in the first light-scattering layer and a thickness D 1  of the first light-scattering layer satisfy D 1 /L 1 &lt;15.

FIELD

The present invention relates to an organic EL light-emitting device.Herein, the “organic EL” is an abbreviation of “organicelectroluminescence”.

BACKGROUND

An organic EL light-emitting device having a plurality of electrodelayers and a light-emitting layer disposed therebetween to generateelectrical light has been studied for its use as a display device thatcan be a substitute for a liquid crystal cell. The organic ELlight-emitting device has also been studied as to its use for a surfacelight source device such as planar lighting and a backlight for a liquidcrystal display device, taking advantages of its characteristics such ashigh light-emitting efficiency, low-voltage drive, lightweight, and lowcost.

When the organic EL light-emitting device is used as a light source of asurface light source device, there is a demand for extracting light in auseful state with high efficiency from an element. For example, althoughthe light-emitting layer of the organic EL light-emitting device hashigh light-emitting efficiency, the layers constituting the device mayincur a large amount of loss of light while the light is passing throughthe layer before the light emission, depending on conditions such as arefractive index difference between the layers. Therefore, there is ademand for keeping the loss of light as small as possible.

As a method for increasing light extraction efficiency, for example,provision of many concave portions or convex portions on alight-emitting surface of the organic EL light-emitting device has beenknown. For example, Patent Literature 1 proposes that pyramidal concaveportions are formed on a light-emitting surface of an organic ELlight-emitting device, by which improvement in the light extractionefficiency is expected.

CITATION LIST Patent Literature

Patent Literature 1: WO2012/002260 A1

SUMMARY Technical Problem

However, formation of pyramidal concave or convex portions on alight-emitting surface may cause increase of the production cost.Therefore, a technology for enhancing the light extraction efficiency ofan organic EL light-emitting device while suppressing increase ofproduction cost is required.

As the technology for enhancing the light extraction efficiency whilesuppressing the increase of production cost, formation of aconcavo-convex structure in a streak array pattern on a light-emittingsurface of an organic EL light-emitting device can be considered. Theconcavo-convex structure in a streak array pattern can be easilyproduced by smaller number of steps than that of steps of formingpyramidal concave and convex portions. Therefore, the concavo-convexstructure in a streak array pattern can be produced usually at a lowercost than that for the formation of the pyramidal concave and convexportions. However, it is difficult to enhance the light extractionefficiency of an organic EL light-emitting device having theconcavo-convex structure in a streak array pattern on a light-emittingsurface to the same level as the light extraction efficiency of anorganic EL light-emitting device having the pyramidal concave or convexportions on a light-emitting surface.

The present invention has been made in view of the aforementionedproblems, and an object of the present invention is to provide anorganic EL light-emitting device having a concavo-convex structure in astreak array pattern and having excellent light extraction efficiency.

Solution to Problem

The present inventor has intensively studied to solve the aforementionedproblems. As a result, the inventor has found that the light extractionefficiency of an organic EL light-emitting device including alight-emitting layer, a light-scattering structure and a concavo-convexstructure in a streak array pattern in this order can be enhanced when alight-scattering layer containing light-scattering particles and abinder is provided between the light-scattering structure and theconcavo-convex structure so as to satisfy predetermined requirements,thereby completing the present invention.

Specifically, the present invention is as follows.

(1) An organic EL light-emitting device comprising: a light-emittinglayer capable of generating light; a light-scattering structure capableof scattering the light; a first light-scattering layer containing firstlight-scattering particles having an average particle diameter of 0.1 μmto 2 μm and a first binder; and a concavo-convex structure in a streakarray pattern, the light emitting layer, the light-scattering structure,the first light-scattering layer, and the concavo-convex structure beingdisposed in this order, wherein

a mean free path L1 of light scattering in the first light-scatteringlayer and a thickness D1 of the first light-scattering layer satisfyD1/L1<15.

-   (2) The organic Em light-emitting device according to (1), wherein

the average particle diameter of the first light-scattering particles is0.4 μm to 1 μm, and

D1/L1<6.

-   (3) The organic EL light-emitting device according to (1) or (2),    wherein

the light-scattering structure is a second light-scattering layercontaining second light-scattering particles, and

a mean free path L2 of light scattering in the second light-scatteringlayer and a thickness D2 of the second light-scattering layer satisfy(D1/L1+D2/L2)<6.

-   (4) The organic EL light-emitting device according to (3), wherein a    ratio of the second light-scattering particles in the second    light-scattering layer is 0.5% by weight or more and 40% by weight    or less.-   (5) The organic EL light-emitting device according to (3) or (4),    wherein an average particle diameter of the second light-scattering    particles is 0.2 μm or more and 2 μm or less.-   (6) The organic EL light-emitting device according to any one of (1)    to (5), wherein the concavo-convex structure includes a prism.-   (7) The organic EL light-emitting device according to (6), wherein    the prism has an apex angle of 80° or smaller.-   (8) The organic EL light-emitting device according to any one of (1)    to (7), wherein the first binder has a refractive index of 1.5 or    more.-   (9) The organic EL light-emitting device according to any one of (1)    to (8), wherein the first binder contains high refractive index    nanoparticles.-   (10) The organic EL light-emitting device according to (9), wherein    the high refractive index nanoparticles are contained in a ratio of    20% by weight or more and 80% by weight or less relative to a total    amount of the first binder.-   (11) The organic EL light-emitting device according to any one    of (1) to (10), wherein the first light-scattering layer has    adhesiveness.

Advantageous Effects of Invention

The present invention can provide an organic EL light-emitting devicethat has a concavo-convex structure in a streak array pattern and isexcellent in light extraction efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically showing an organic ELlight-emitting device according to a first embodiment of the presentinvention.

FIG. 2 is a cross-sectional view schematically showing a cross sectionof a concavo-convex structure layer of the organic EL light-emittingdevice according to the first embodiment of the present invention.

FIG. 3 is a graph showing a relationship between the mean free path of alight-scattering layer according to an example and the particle diameterof light scattering particles contained in the light-scattering layer.

FIG. 4 is a perspective view schematically showing an organic ELlight-emitting device according to a second embodiment of the presentinvention.

FIG. 5 is a plan view schematically showing a light-emitting surface ofa concavo-convex structure layer according to an example.

FIG. 6 is a graph showing a relationship between D1/L1 and the totallight flux obtained by simulation according to Example 3 of the presentinvention.

FIG. 7 is a diagram showing a relationship between D1/L1 and D2/L2 andthe total light flux obtained by simulation according to Example 4 ofthe present invention.

FIG. 8 is a graph showing a relationship between the apex angle ofprisms and the total light flux obtained by simulation according toExample 5 of the present invention.

FIG. 9 is a graph showing a relationship between the concentration oflight-scattering particles and D/L obtained in Reference Example 1.

DESCRIPTION OF EMBODIMENTS

Although the present invention will be described below in detail by wayof embodiments and examples, the present invention is not limited to theembodiments, the examples, and the like described below and may befreely modified for implementation without departing from the scope ofthe claims of the present invention and equivalents thereto.

1. First Embodiment

FIG. 1 is a perspective view schematically showing an organic ELlight-emitting device 100 according to a first embodiment of the presentinvention.

As shown in FIG. 1, the organic EL light-emitting device 100 accordingto the first embodiment of the present invention is a device foremitting light generated within the organic EL light-emitting device 100through a light-emitting surface 100U. This organic EL light-emittingdevice 100 includes a light-emitting surface structure layer 110, afirst light-scattering layer 120, a substrate plate layer 130 as asupporting substrate plate, a second light-scattering layer 140 as alight-scattering structure, a light-emitting element layer 150, and asealing layer 160 in this order from a side close to the light-emittingsurface 100U. The light-emitting surface structure layer 110 has aconcavo-convex structure layer 111 having a concavo-convex structure 170in a streak array pattern, and a substrate film layer 112. Herein the“concavo-convex structure in a streak array pattern” represents a groupof a plurality of concave portions or convex portions that are providedside by side, wherein each portion continuously extends over a certainlength. The light-emitting element layer 150 includes a transparentelectrode layer 151 as a first electrode layer, a reflecting electrodelayer 153 as a second electrode layer, and a light-emitting layer 152provided between the transparent electrode layer 151 and the reflectingelectrode layer 153.

The organic EL light-emitting device 100 includes the sealing layer 160,the reflecting electrode layer 153, the light-emitting layer 152, thetransparent electrode layer 151, the second light-scattering layer 140,the substrate plate layer 130, the first light-scattering layer 120, thesubstrate film layer 112, and the concavo-convex structure layer 111 inthis order in the thickness direction of the organic EL light-emittingdevice 100. Therefore., light generated in the, light-emitting layer 152passes through the transparent electrode layer 151, or is reflected bythe reflecting electrode layer 153 and then passes through thelight-emitting layer 152 and the transparent electrode layer 151.Subsequently, the light passes through the second light-scattering layer140, the substrate plate layer 130, the first light-scattering layer120, the substrate film layer 112, and the concavo-convex structurelayer 111, and exits through the light-emitting surface 100U.

[1.1. Light-Emitting Surface Structure Layer 110]

The light-emitting surface structure layer 110 includes theconcavo-convex structure layer 111 and the substrate film layer 112. Asurface of the light-emitting surface structure layer 110 on a sideopposite to the light-emitting element layer 150 is a surface of theconcavo-convex structure layer 111 on a side opposite to the substratefilm layer 112, and is exposed at the outermost surface of the organicEL light-emitting device 100. The surface of the concavo-convexstructure layer 111 on the side opposite to the substrate film layer 112is thus the light-emitting surface 100U of the organic EL light-emittingdevice 100, that is, the light-emitting surface 100U through which lightexits from the organic EL light-emitting device 100 to the outside ofthe device.

The concavo-convex structure layer 111 has the concavo-convex structure170 in a streak array pattern on the light-emitting surface 100U.Therefore, the light-emitting surface 100U is not a flat surface from amacroscopic viewpoint. However, since the concave portions and theconvex portions included in the concavo-convex structure 170 are small,the light-emitting surface 100U may be a flat surface parallel to aprincipal plane of the organic EL light-emitting device 100 when viewingthe light-emitting surface 100U macroscopically. Therefore, beingparallel or perpendicular to the light-emitting surface 100U in thefollowing description means being parallel or perpendicular to thelight-emitting surface 100U from a macroscopic viewpoint without takingconcave or convex portions into consideration, unless otherwisespecified. In this embodiment, unless otherwise specified, the organicEL light-emitting device 100 is described in a state where thelight-emitting surface 100U is disposed in parallel to the horizontaldirection and faces upward. Further, “parallel” or “perpendicular”relationship of constituent members may include instances having anerror within a rage that does not impair the effects of the presentinvention, for example, within a range of ±5°.

The concavo-convex structure 170 in a streak array pattern formed on thelight-emitting surface 100U includes a plurality of concave portions andconvex portions each of which extends in a direction parallel to thelight-emitting surface 100U. All of the concave portions or the convexportions usually extend in the same direction. Though the concaveportions or the convex portions may be formed at intervals as long asthe effects of the present invention are not remarkably impaired, theconcave portions or the convex portions are usually formed side by sidewith no spacing therebetween. The shape of the concave portions or theconvex portions may be freely determined. For example, a cross-sectionalshape obtained by cutting the concave portions or the convex portions ona plane perpendicular to the extending direction of the concave portionsor the convex portions may be polygonal, and may also be a part of acircle or an ellipse. Specifically, when the aforementionedcross-sectional shape is a triangle, the concave portion or the convexportion forms a prism. When the aforementioned cross-sectional shape isa part of a circle or an ellipse, the concave portion or the convexportion forms a lenticular lens.

In this embodiment, an example where the concavo-convex structure 170consists of a group of prisms 171 as a plurality of convex portionsextending in one direction will be described. The cross-sectional shapeof each of the prisms 171 obtained by cutting the prisms 171 on a planeperpendicular to the direction in which the prisms 171 extend is anisosceles triangle. The prisms 171 are disposed in parallel to eachother with no spacing therebetween on the entire light-emitting surface100U.

FIG. 2 is a cross sectional view schematically showing a cross sectionof the concavo-convex structure layer 111 of the organic ELlight-emitting device 100 according to the first embodiment of thepresent invention.

As shown in FIG. 2, the apex angle θ₁₇₁ of the prisms 171 contained inthe convex-concave structure 170 is preferably 10° or larger, morepreferably 20° or larger, and particularly preferably 30° or larger, andis preferably 80° or smaller, more preferably 70° or smaller, andparticularly preferably 65° or smaller. When the apex angle θ₁₇₁ of theprisms 171 is equal to or larger than the lower limit of theabove-described range, damage to the prisms 171 can be suppressed. Whenit is equal to or smaller than the upper limit, the light extractionefficiency of the organic EL light-emitting device 100 can be enhanced.

The size of the prisms 171 may be optionally set as long as the effectsof the present invention are not remarkably impaired. For example, thepitch P₁₇₁ between the prisms 171 is usually 1 μm or more, preferably 5μm or more, and more preferably 10 μm or more, and is usually 500 μm orless, preferably 100 μm or less, and more preferably 50 μm or less. Theheight (or depth) H₁₇₁ of the prisms 171 is usually 1 μm or more,preferably 5 μm or more, and more preferably 10 μm or more, and isusually 500 μm or less, preferably 100 μm or less, and more preferably50 μm or less. When the size of the prisms 171 falls within the range,the light extraction efficiency of the organic EL light-emitting device100 can be enhanced.

As an example of a material for the concavo-convex structure layer 111,a transparent material is usually used. Herein, a material being“transparent” means that the material has a light transmittance thatsuitable to be used for an optical member. For example, the total lighttransmittance of the material in terms of a thickness of 1 mm is usually80% or more, and preferably 90% or more. The total light transmittancecan be measured in accordance with JIS K7361-1997.

Specific examples of the transparent material may include a variety oftypes of resins. Examples of the resins may include a thermoplasticresin; a thermosetting resin; and an energy ray curable resin such as anultraviolet curable resin and an electron beam curable resin. Amongthese, a thermoplastic resin is preferred since it is easily deformed byheat. An ultraviolet curable resin is preferred since it has highcurability and favorable efficiency to allow efficient formation of theconcavo-convex structure layer 111. Examples of the thermoplastic resinmay include a polyester resin, a polyacrylate resin, and a cycloolefinresin. Examples of the ultraviolet curable resin may include an epoxyresin, an acrylic resin, a urethane resin, an ene/thiol resin, and anisocyanate resin. It is preferable that these resins contain a polymerhaving a plurality of polymerizable functional groups. One type thereofmay be used alone, or two or more types thereof may be used incombination at any ratio.

It is preferable that the material for the concavo-convex structurelayer 111 is a material capable of having a high hardness by curingsince therewith the concavo-convex structure 170 can be easily formedand scratch resistance can be easily imparted to the concavo-convexstructure 170. Specifically, it is preferable that the material has apencil hardness of equal to or more than HB, further preferably equal toor more than H, and more preferably equal to or more than 2H. The pencilhardness is measured for a layer having a film thickness of 7 μm and noconcavo-convex structure.

The thickness T₁₁₁ of the concavo-convex structure layer 111 ispreferably 1 μm or more, and more preferably 5 μm or more, and may be 10μm or more. The thickness T₁₁₁ of the concavo-convex structure layer 111is preferably 500 μm or less, and more preferably 100 μm or less, andmay be 50 μm or less. When the thickness T₁₁₁ of the concavo-convexstructure layer 111 is equal to or less than the upper limit of theabove-described range, deformation like curling of the concavo-convexstructure layer 111 caused by curing shrinkage can be prevented and theconcavo-convex structure layer 111 of a favorable shape can be achieved.

The substrate film layer 112 shown in FIG. 1 is a optional layer, andusually includes a film formed of a transparent material. The substratefilm layer 112 may be formed of the same material as that for theconcavo-convex structure layer 111. However, when the substrate filmlayer 112 is formed of a material different from that for theconcavo-convex structure layer 111, the light-emitting surface structurelayer 110 having a variety of characteristics can be obtained. Forexample, it is preferable that the concavo-convex structure layer 111 isformed or a material having a high hardness and the substrate film layer112 is formed of a flexible material. By combination of the materials asdescribed above, the handleability of the substrate film layer 112during formation of the concavo-convex structure layer 111 can beimproved. The handleability of the light-emitting surface structurelayer 110 after the formation of the concavo-convex structure layer 111can also be enhanced. Further, the durability of the light-emittingsurface structure layer 110 can also be enhanced. Consequently, theorganic EL light-emitting device 100 having high performance can beeasily produced.

Examples of the material for the substrate film layer 112 may include analicyclic olefin polymer and a polyester. One type thereof may be usedalone, or two or more types thereof may be used in combination at anyratio.

The refractive index of the substrate film layer 112 is preferably closeto the refractive index of a binder of the first light-scattering layer120. Hereinafter, the binder of the first light-scattering layer 120 maybe appropriately referred to as “first, binder”. Specifically, adifference between the refractive index of the substrate film layer 112and the refractive index of the first binder is preferably 0.15 or less,more preferably 0.1 or less, and further preferably 0.03 or less. Inthis manner, the light extraction efficiency of the organic ELlight-emitting device 100 can be enhanced. Herein, one refractive indexmay be measured by an ellipsometer (for example, “M-2000” manufacturedby J. A. Woollam Japan).

The thickness of the substrate film layer 112 is preferably 20 μm to 300μm.

The method for producing the aforementioned light-emitting surfacestructure layer 110 is not limited. For example, the light-emittingsurface structure layer 110 may be produced by forming theconcavo-convex structure layer 111 on a surface 112U of the substratefilm layer 112 by a photopolymer method (2P method) using theaforementioned material for the concavo-convex structure layer 111.

[1.2. First Light-Scattering Layer 120]

(1.2.1. Requirements satisfied by First Light-Scattering Layer 120)

As shown in FIG. 1, the first light-scattering layer 120 is a layerprovided between the concavo-convex structure layer 111 and the secondlight-scattering layer 140, and includes first light-scatteringparticles and the first binder. The first light-scattering layer 120satisfies the following requirements (R) and (B).

Requirement (A): The average particle diameter of the firstlight-scattering particles is 0.1 μm to 2 μm.

Requirement (B): The mean free path L1 of light scattering in the firstlight-scattering layer 120 and the thickness D1 of the firstlight-scattering layer 120 satisfy D1/L1<15.

When the organic EL light-emitting device 100 includes the firstlight-scattering layer 120 that satisfies the requirements (A) and (B)described above in combination with the second light-scattering layer140 as the light-scattering structure, high light extraction efficiencycan be achieved even if the concavo-convex structure in a streak arraypattern is employed as the concavo-convex structure 170 formed on theconcavo-convex structure layer 111.

Hereinafter, these requirements will be described in detail.

The requirement (A) will be first described.

The average particle diameter of the first light-scattering particles isusually 0.1 μm or more, preferably 0.4 μm or more, and more preferably0.5 μm with or more, and is usually 2 μm or less, preferably 1 μm orless, and more preferably 0.9 μm or less. Unless otherwise specified,the average particle diameter herein refers to a volume average particlediameter. The volume average particle diameter represents a particlediameter at which a cumulative volume calculated from a small-diameterside in a particle diameter distribution measured by a laser diffractionmethod reaches 50%. When the average particle diameter of the firstlight-scattering particles is equal to or more than the lower limit ofthe above-described range, the particle diameter of the firstlight-scattering particles can be stably made longer than the wavelengthof light to be scattered. Therefore, visible light can be stablyscattered by the first light-scattering particles. When the averageparticle diameter is equal to or less than the upper limit, the particlediameter can be decreased. Therefore, light that reaches the firstlight-scattering particles can be reflected to a wide region.Accordingly, visible light can be efficiently scattered by the firstlight-scattering particles.

The requirement (B) will now be described.

In the first light-scattering layer 120, D1/L1 is usually less than 15,preferably less than 6, and more preferably less than 4.5. When D1/L1falls within such a range, the light extraction efficiency of theorganic EL light-emitting device 100 can be effectively enhanced.Herein, “D1” represents the thickness of the first light-scatteringlayer 120. “L1” represents the mean free path of light scattering in thefirst light-scattering layer 120. The lower limit of D1/L1 is notparticularly limited, and is usually more than 0, preferably more than0.5, and more preferably more than 1.0. In this manner, the lightextraction efficiency can be enhanced similarly to the case of the upperlimit.

In general, the mean free path L of light scattering in alight-scattering layer containing a binder and light-scatteringparticles dispersed in the binder is calculated by “mean free pathL=1/(number density of light-scattering particles×scattering crosssection)”.

The number density of the light-scattering particles is the number ofthe light-scattering particles per unit volume. In calculation of numberdensity of the light-scattering particles, the volume per particle ofthe light-scattering particles is usually used. When the volume perparticle of the light-scattering particles is calculated, the particlediameter of the light-scattering particles may be used. Since theparticle diameter of the light-scattering particles is usuallydistributed in a certain range, the volume average particle diameter ofthe light-scattering particles may be used as a representative value forthe particle diameter used in calculation of number density of thelight-scattering particles. In order to simplify the calculation ofvolume per particle of the light-scattering particles, the shape of thelight-scattering particles is assumed to be a sphere for calculation.

The scattering cross section may be obtained by Mie scattering theory(MIE THEORY). The Mie scattering theory is that the solution ofMaxwell's electromagnetic equations is determined in a case where amedium (matrix) having a uniform refractive index contains sphericalparticles having a refractive index different from that of the medium.The spherical particles correspond to the light-scattering particles,and the medium corresponds to the binder. In accordance with thistheory, the aforementioned scattering cross section is calculated by“scattering cross section=scattering efficiency K(α)×actualcross-section area of spherical particles πr²”.

Herein, the intensity distribution I (α, θ) that depends on the angle ofscattering light is represented by the following equation (1). Thescattering efficiency K(α) is represented by the following equation (2).Further, α is represented by the following equation (3). It is an amountcorresponding to the radius r of the spherical particles normalized bythe wavelength λ of light in the medium. The angle θ is a scatteringangle. The angle θ in the traveling direction of incident light is 180°.i₁ and i₂ the equation (1) are represented by the equation (4). a and bwith subscript v in the equations (2) to ( )are represented by theequation (5). P (cos θ) with superscript 1 and subscript υ consists ofLegendre's polynomials. a and b with subscript υ consist ofRecatti-Bessel functions Ψ_(υ) and ζ_(υ) that are linear and quadratic(provided that _(υ) means subscript υ) and derived functions thereof. mis a relative refractive index of the spherical particles on the basisof the matrix, and m=n_(scatter)/n_(matrix). n_(scatter) represents therefractive index of the spherical particles. n_(matrix) represents therefractive index of the medium.

$\begin{matrix}{{I( {\alpha,\theta} )} = {\frac{\lambda^{2}}{8\pi^{2}}( {i_{1} + i_{2}} )}} & (1) \\{{K(\alpha)} = {( \frac{2}{\alpha^{2}} ){\sum\limits_{v = 1}^{\infty}{( {{2v} + 1} )( {{a_{v}}^{2} + {{b_{v}}^{2}}} )}}}} & (2) \\{\alpha = {2\pi \; {r/\lambda}}} & (3) \\{{i_{1} = {{\sum\limits_{v = 1}^{\infty}{\frac{{2v} + 1}{v( {v + 1} )}\{ {{a_{v}\frac{P_{v}^{1}( {\cos \; \theta} )}{\sin \; \theta}} + {b_{v}\frac{{dP}_{v}^{1}( {\cos \; \theta} )}{d\; \theta}}} \}}}}^{2}}{i_{2} = {{\sum\limits_{v = 1}^{\infty}{\frac{{2v} + 1}{v( {v + 1} )}\{ {{b_{v}\frac{P_{v}^{1}( {\cos \; \theta} )}{\sin \; \theta}} + {a_{v}\frac{{dP}_{v}^{1}( {\cos \; \theta} )}{d\; \theta}}} \}}}}^{2}}} & (4) \\{{a_{v} = \frac{{{\Psi_{v}^{\prime}( {m\; \alpha} )}{\Psi_{v}(\alpha)}} - {m\; {\Psi_{v}( {m\; \alpha} )}{\Psi_{v}^{\prime}(\alpha)}}}{{{\Psi_{v}^{\prime}( {m\; \alpha} )}{Ϛ_{v}(\alpha)}} - {m\; {\Psi_{v}( {m\; \alpha} )}{Ϛ_{v}^{\prime}(\alpha)}}}}{b_{v} = \frac{{m\; {\Psi_{v}^{\prime}( {m\; \alpha} )}{\Psi_{v}(\alpha)}} - {{\Psi_{v}( {m\; \alpha} )}{\Psi_{v}^{\prime}(\alpha)}}}{{m\; {\Psi_{v}^{\prime}( {m\; \alpha} )}{Ϛ_{v}(\alpha)}} - {{\Psi_{v}( {m\; \alpha} )}{Ϛ_{v}^{\prime}(\alpha)}}}}} & (5)\end{matrix}$

For example, the mean free path L of the light-scattering layercontaining a binder having a refractive index of 1.56 and about 10.6% byweight (8% by volume) of silicone particles as light-scatteringparticles having a refractive index of 1.43 is calculated by theaforementioned method using light that has a wavelength of 550 nm in avacuum, whereby the result as shown in FIG. 3 is obtained. The examplein FIG. 3 shows the mean free path L for a case where the particlediameter of the light-scattering particles is changed to 200 nm, 600 nm,1,000 nm, 1,500 nm, and 2,000 nm while the volume concentration of thelight-scattering particles in the light-scattering layer is constant. Incalculation of number density [particles/mm³] of the light-scatteringparticles, the specific gravity of the binder is assumed to be 1 g/cm³,and the specific gravity of the light-scattering particles is assumed tobe 1.32 g/cm³. The shape of the light-scattering particles is assumed tobe a sphere. The assumption that the shape of the light-scatteringparticles is a sphere can be applied to cases where the shape of actuallight-scattering particles is close to a sphere. Further, even in caseswhere the shape of actual light-scattering particles is not close to asphere, the mean free path L tends to change depending on the particlediameter size of the light-scattering particles, and thus similartendencies are expected.

(1.2.2. First Light-Scattering Particles)

Any light-scattering particles may be used as the first light-scatteringparticles as long as the aforementioned requirements and (B) aresatisfied. The light-scattering particles are particles capable ofscattering light. With the first light-scattering particles, lightpassing through the first light-scattering layer 120 is scattered,whereby the light extraction efficiency of the organic EL light-emittingdevice 100 can be enhanced.

For the first light-scattering particles, an inorganic material or anorganic material may be used.

Examples of the inorganic material for the first light-scatteringparticles may include metals and metal compounds. Examples of the metalcompounds may include oxides and nitrides of metals. Specific examplesthereof may include metal such as silver and aluminum; and metalcompounds such as silicon oxide, aluminum oxide, zirconium oxide,silicon nitride, tin-doped indium oxide, and titanium oxide.

Examples of the organic material for the first light-scatteringparticles may include resins such as a silicone resin, an acrylic resin,and a polystyrene resin.

One type of the material for the first light-scattering particles may beused alone, or two or more types thereof may be used in combination atany ratio.

Of these, the first light-scattering particles formed of the organicmaterial are preferred as the first light-scattering particles. Thefirst light-scattering layer 120 is usually produced using a coatingliquid suitable for production of the first light-scattering layer 120.The first light-scattering particles are likely to settle in the coatingliquid. In particular, first light-scattering particles containinginorganic particles having high specific gravity are likely to settle.In contrast, first light-scattering particles formed of the organicmaterial are unlikely to settle. Therefore, by using the firstlight-scattering particles formed of the organic material, the firstlight-scattering layer 120 that contains the first light-scatteringparticles homogeneously and evenly can be obtained. Such a firstlight-scattering layer 120 containing the first light-scatteringparticles homogeneously is preferred since it can stably exhibitcharacteristics such as adhesiveness.

Suitable examples of the first light-scattering particles formed of theorganic material will be exemplified with trade names. Examples ofparticles formed of a silicone resin may include a product with a tradename of “XC-99” (available from Momentive Performance Materials Inc.,volume average particle diameter: 0.7 μm). Examples of particles formedof an acrylic resin may include a product with a trade name of “MPseries” (available from Soken Chemical & Engineering Co., Ltd., volumeaverage particle diameter: 0.8 μm). Examples of particles formed of apolystyrene resin may include a product with a trade name of “SX series”(available from Soken Chemical & Engineering Co., Ltd., volume averageparticle diameter: 3.5 μm).

One type of the first light-scattering particles may be used alone, ortwo or more types thereof may be used in combination at any ratio.

The refractive index of the first light-scattering particles is usually1.2 or more, preferably 1.3 or more, and more preferably 1.4 or more,and is usually 1.55 or less, preferably 1.5 or less, and more preferably1.45 or less. When the refractive index of the first light-scatteringparticles is equal to or more than the lower limit of theabove-described range, variation of scattering property due tofluctuation of the particle diameter and the film thickness can besuppressed. When the refractive index is equal to or less than the upperlimit, light can be sufficiently scattered.

The ratio of the first light-scattering particles in the firstlight-scattering layer 120 is preferably 0.5% by weight or more, andmore preferably 3% by weight or more, and is preferably 40% by weight orless, and more preferably 20% by weight or less. When the ratio of thefirst light-scattering particles falls within the above-described range,the light extraction efficiency of the organic EL light-emitting device100 can be effectively enhanced. Further, a desired light-scatteringeffect can be usually obtained to suppress color unevenness depending ona polar angle direction on the light-emitting surface 100U.

(1.2.3. First Binder)

Any material may be used as the first binder as long as theaforementioned requirements (A) and (B) are satisfied. The first binderhas a function of holding the first light-scattering particles in thefirst light scattering lager 120. The first light-scattering particlesof the first light-scattering layer 120 are dispersed in the firstbinder. The first binder is usually transparent. Light passing throughthe transparent first binder may be reflected on the interface betweenthe first binder and the first light-scattering particles so as to bescattered.

As the first binder, those having adhesiveness are preferably used.Thereby adhesiveness can be imparted to the first light-scattering layer120. When the first light-scattering layer 120 has adhesiveness, thelight-emitting surface structure layer 110 and the substrate plate layer130 can be easily bonded through the first light-scattering layer 120.Consequently, the organic EL light-emitting device 100 can be easilyproduced.

As the first binder having such adhesiveness, a resin is usually used.Examples of the resins may include an adhesive containing a polymer asan adhesive material having adhesiveness. Herein the “adhesive” includesnot only an adhesive in the narrow sense but also a hot-melt adhesive.Herein, the adhesive in the narrow sense is an adhesive that has a shearstorage elastic modulus at 23° C. of less than 1 MPa and showsadhesiveness at normal temperature. Herein, the hot-melt adhesive is anadhesive that has a shear storage elastic modulus at 23° C. of 1 MPa to500 MPa and does not show adhesiveness at normal temperature. It isparticularly preferable that the adhesive for use is an adhesive in thenarrow sense showing adhesiveness at normal temperature. Such anadhesive in the narrow sense is a pressure-sensitive adhesive with whichadhesion can be effected by application of pressure. The adhesive allowsbonding in a simple manner without giving any influences caused byheating, such as deterioration, to the light-emitting layer 152.

Examples of the adhesives may include a rubber-based adhesive, anacrylic adhesive, a silicone-based adhesive, a urethane-based adhesive,a vinyl alkyl ether-based adhesive, a polyvinyl alcohol-based adhesive,a polyvinyl pyrrolidone-based adhesive, a polyacrylamide-based adhesive,and a cellulose-based adhesive. One type thereof may be used alone, ortwo or more types thereof may be used in combination at any ratio. Inparticular, an acrylic adhesive is preferred since the adhesive isexcellent in characteristics such as transparency, weather resistance,and heat resistance.

The acrylic adhesive usually contains an acrylic polymer as an adhesivematerial. The acrylic polymer is a polymer containing a structure unithaving a structure formed by polymerization of an acrylic monomer.Examples of the acrylic polymer may include a polymer obtained bypolymerization of an acrylic monomer; and a polymer obtained bypolymerization of a mixture (monomer mixture) of an acrylic monomer witha monomer copolymerizable with the acrylic monomer.

Examples of the acrylic monomer may include alkyl (meth) acrylate.Herein, (meth) acrylate includes acrylate, methacrylate, and acombination thereof. The average number or carbon atoms or alkyl groupof alkyl (meth) acrylate is preferably 1 or more, and more preferably 3or more, and is preferably 12 or less, and more preferably 8 or less.Specific examples of alkyl (meth) acrylate may include methyl (meth)acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl(meth) acrylate, and isooctyl (meth) acrylate. One type thereof may beused alone, or two or more types thereof may be used in combination atany ratio.

Preferable examples of the monomer copolymerizable with the acrylicmonomer may include a monomer having a functional group, a nitrogenatom-containing monomer, and a modifying monomer.

Examples of the monomer having a functional group may include a monomerhaving a carboxyl group, a monomer having a hydroxyl group, and amonomer having an epoxy group. Examples of the monomer having a carboxylgroup may include acrylic acid, methacrylic acid, fumaric acid, maleicacid, and itaconic acid. Examples of the monomer having a hydroxyl groupmay include 2-hydroxyethyl (meth) acrylate, hydroxybutyl (meth)acrylate,hydroxyhexyl (meth) acrylate, and N-methylol (meth) acrylamide. Examplesof the monomer having an epoxy group may include glycidyl (meth)acrylate. When the acrylic monomer and the monomer having a functionalgroup are used in combination, it is preferable that the ratio of theacrylic monomer is 60% by weight to 99.8% by weight and the ratio of themonomer having a functional group is 40% by weight to 0.2% by weightrelative to 100% by weight of the sum of the acrylic monomer and themonomer having a functional group.

Examples of the nitrogen atom-containing monomer may include(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, (meth)acryloylmorpholine, (meth)acetonitrile, vinyl pyrrolidone, N-cyclohexylmaleimide, itaconimide, andN,N-dimethylaminoethyl(meth)acrylamide. When the acrylic monomer and thenitrogen atom-containing monomer are used in combination, it ispreferable that the ratio of the acrylic monomer is 60% by weight to99.8% by weight and the ratio of the nitrogen atom-containing monomer is40% by weight to 0.2% by weight relative to 100% by weight of the sum ofthe acrylic monomer and the nitrogen atom-containing monomer.

Examples of the modifying monomer may include vinyl acetate and styrene.When the acrylic monomer and the modifying monomer are used incombination, it is preferable that the ratio of the acrylic monomer is60% by weight to 99.8% by weight and the ratio of the modifying monomeris 40% by weight to 0.2% by weight relative to 100% by weight of the sumof the acrylic monomer and the modifying monomer.

One type of the monomer copolymerizable with the acrylic monomer may beused alone, or two or more types thereof may be used in combination atany ratio.

The amount of the polymer as the adhesive material relative to the totalamount of the first binder is preferably 10% by weight or more, and morepreferably 20% by weight or more, and is preferably 80% by weight orless, and more preferably 70% by weight or less.

Th first binder monomer may contain high refractive index nanoparticles.When the high refractive index nanoparticles are used, the refractiveindex of the first binder can be easily adjusted. For example, by addingthe high refractive index nanoparticles to an adhesive having a lowrefractive index, the refractive index of the adhesive can be increased.As the high refractive index nanoparticles, particles that have a smallaverage particle diameter and higher refractive index than that of theadhesive not containing high refractive index nanoparticles are usuallyused. Specifically, particles that have a volume average particlediameter of less than 100 nm and a refractive index of 1.6 or more maybe used.

Examples of the high refractive index nanoparticles may includeparticles formed of an inorganic material and particles formed of anorganic material having a refractive index of 1.6 or more. Examples ofthe inorganic material may include oxides such as zirconia, titania, tinoxide, and zinc oxide; titanates such as barium titanate and strontiumtitanate; and sulfides, selenides, and tellurides such as CdS, CdSe,CdTe, ZnS, HgS, HgSe, PdS, and SbSe. Examples of the organic materialhaving a refractive index of 1.6 or more may include a polystyreneresin. One type thereof may be used alone, or two or more types thereofmay be used in combination at any ratio. The surface of the highrefractive index nanoparticles may be modified kith a variety of typesof functional group for increasing dispersibility, a silane couplingagent, or the like.

Among these, it is preferable that the high refractive indexnanoparticles are reactive modified metal oxide particles. The reactivemodified metal oxide particles are particles containing a metal oxideand an organic substance that modifies the surface of the metal oxideand has a reactive functional group. Specifically, the reactive modifiedmetal oxide particles are coated particles containing particles of metaloxide and an organic substance that modifies the surface of theparticles and that has a reactive functional group.

The reactive functional group in the organic substance having a reactivefunctional group may he in a state in which the reactive functionalgroup has an interaction with the particles of metal oxide, such as ahydrogen bond. Alternatively, the reactive functional group may not bein such a state but in a state in which the reactive functional groupcan interact with another substance.

Examples of the reactive functional group may include a hydroxyl group,a phosphoric acid group, a carboxyl group, an amino group, an alkoxygroup, an isocyanate group, an acid halide, an acid anhydride, aglycidyl group, a chlorosilane group, and an alkoxysilane group. Onetype thereof may be used alone, or two or more types thereof may be usedin combination at any ratio.

It is particularly preferable that the organic substance having areactive functional group is an organic substance having an isocyanategroup since the stability of the metal oxide and a surrounding substancemay be improved. Examples of the organic substance having an isocyanategroup may include acryloxymethyl isocyanate, methacryloxymethylisocyanate, acryloxyethyl isocyanate, methacryloxyethyl isocyanate,acryloxypropyl isocyanate, methacryloxypropyl isocyanate, and1,1-bis(acryloxymethyl)ethyl isocyanate. One type thereof may be usedalone, or two or more types thereof may be used in combination at anyratio.

Examples of the metal oxide contained in the reactive modified metaloxide particles may include titanium oxide, zinc oxide, zirconium oxide,antimony oxide, tin-doped indium oxide (ITO), antimony-doped tin oxide(ATO), fluorine-doped tin oxide (FTO), phosphorus-doped tin oxide (PTO),zinc antimonate (AZO), indium-doped zinc oxide (IZO), aluminum-dopedzinc oxide, gallium-doped zinc oxide, cerium oxide, aluminum oxide, andtin oxide. One type thereof may be used alone, or two or more typesthereof may be used in combination at any ratio.

The ratio of the organic substance having a reactive functional group inthe reactive modified metal oxide particles may be 1 part by weight to40 parts by weight relative to 100 parts by weight of metal oxide.

The reactive modified metal oxide particles may be obtained as asuspension in which the particles are dispersed in the organic solventby, for example, mixing the particles of metal oxide, the organicsubstance having a reactive functional group, an organic solvent, and ifnecessary, an optional additive, and furthermore if necessary,subjecting the obtained mixture to a treatment such as an ultrasonictreatment.

Examples of the organic solvent may include ketones such as methyl ethylketone, methyl isobutyl ketone, acetone, and cyclohexanone; aromatichydrocarbons such as benzene, toluene, xylene, and ethylbenzene;alcohols such as methanol, ethanol, isopropyl alcohol, n-butanol, andiso-butanol; ethers such as ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, diethyleneglycol monomethyl ether, and diethylene glycol monoethyl ether; esterssuch as ethyl acetate, butyl acetate, ethyl lactate, γ-butyrolactone,propylene glycol monomethyl ether acetate, and propyleneglycol-monoethyl ether acetate; and amides such as dimethylformamide,N,N-dimethylacetoacetamide, and N-methyl pyrrolidone. One type of theorganic solvent may be used alone, or two or more types thereof may beused in combination at any ratio.

Examples of the optional additive may include a metal chelating agent.One type or the additive may be used alone, or two or more types thereofmay be used in combination at any ratio.

When the reactive modified metal oxide particles are obtained as thesuspension in which the particles are dispersed in the organic solvent,it is preferable that the suspension is used as it is in production ofthe first binder from the viewpoint of convenience of production. Inthis case, it is preferable that the aforementioned suspension isadjusted so as to contain the reactive modified metal oxide particles inan amount of 1% by weight to 50% by weight by adjusting conditions suchas the amount of the solvent.

For mixing, a mixer such as a bead mill is preferably used. By themixing, secondary particles or much higher order particles can bepulverized to a degree of primary particles, and the surface of theparticles in the primary particle state can be treated. Thus, a uniformsurface treatment can be performed.

Further, it is preferable that the mixture is subjected to an ultrasonictreatment, if necessary. In the ultrasonic treatment, for example, adevice such as an ultrasonic cleaner, an ultrasonic homogenizer, and anultrasonic dispersion device may be used. By such a treatment, a goodsuspension can be obtained.

As the reactive modified metal oxide particles, commercially availableparticles may be used. Examples of a slurry of reactive modified metaloxide particles containing ZrO₂ as the metal oxide may include a productwith a trade name of “ZR-010” (available from SOLAR CO., Ltd., solvent:methyl ethyl ketone, particle content: 30%, organic substance thatmodifies a surface and has a reactive functional group: isocyanatehaving a polymerizable functional group, volume average particlediameter: 15 nm). Examples of a slurry of reactive modified metal oxideparticles containing TiO₂ as the metal oxide may include a product witha trade name of “NOD-742GTF” (available from Nagase ChemteX Corporation,solvent: polyethylene glycol monomethyl ether, particle content: 30%,volume average particle diameter: 48 nm).

One type of the high refractive index nanoparticles may be used alone,or two or more types thereof may be used in combination at any ratio.

The volume average particle diameter of the high refractive indexnanoparticles is preferably 5 nm or more, more preferably 10 nm or more,and particularly preferably 15 nm or more, and is preferably less than100 nm, and more preferably 50 nm or less. When the volume averageparticle diameter of the high refractive index nanoparticles is equal toor less than the upper limit of the above-described range, coloring ofthe first light-scattering layer can be reduced to improve the lighttransmittance. The high refractive index nanoparticles of such a sizecan be easily dispersed. Herein, when the high refractive indexnanoparticles are aggregated to form secondary particles or higher orderparticles, the range of the volume average particle diameter may be therange of primary particle diameter.

The ratio of the high refractive index nanoparticles relative to thetotal amount of the first binder is preferably 20% by weight or more,and more preferably 30% by weight or more, and is preferably 80% byweight or less, and more preferably 70% by weight or less. When theratio of the high refractive index nanoparticles is equal to or morethan the lower limit of the above-described range, the refractive indexof the first binder can be increased. When it is equal to or less thanthe upper limit, increase in the hardness of the first binder can besuppressed, and decrease in adhesive force can be suppressed. When fineparticles as described above are used as the high refractive indexnanoparticles, the sum total of surface areas of the particles isincreased, and thus the fine particles interact with polymer moleculechains or monomer molecules contained in the first binder. Theinteraction may affect the adhesive force. Therefore, it is preferablethat the amount of the high refractive index nanoparticles falls withinthe aforementioned range.

The first binder may contain a plasticizer. When a plasticizer is used,the viscosity of the first binder can be decreased to increase theadhesiveness of the first light-scattering layer 120. In particular,when the first binder contains the high refractive index nanoparticles,the viscosity of the first binder tends to be increased to decrease theadhesiveness of the first light-scattering layer 120. Therefore, use ofthe plasticizer is preferable.

Examples of the plasticizer may include polybutene, a vinyl ethercompound, a polyether compound (including polyalkylene oxide andfunctionalized polyalkylene oxide), an ester compound, a polyol compound(for example, glycerol), a petroleum resin, a hydrogenated petroleumresin, and a styrene-based compound (for example, α-methylstyrene).Among these, an ester compound ice, preferred since the miscibility withthe adhesive material is good and the refractive index is comparativelyhigh. In particular, an ester compound having an aromatic ring, such asa benzoic acid-based compound and a phthalic acid-based compound, ispreferred.

Examples or the benzoic acid ester that may be used as the plasticizermay include diethylene glycol dibenzoate, dipropylene glycol dibenzoate,benzyl benzoate, and 1,4-cyclohexane dimethanol dibenzoate. Among these,particularly preferable examples thereof may include benzoic acid-basedester compounds such as dipropylene glycol dibenzoate and benzylbenzoate; and phthalic acid-based ester compounds such as dimethylphthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate,dicyclohexyl phthalate, and ethylphthalyl ethyl glycolate. Examples ofthe commercially available plasticizer may include a product with atrade name of “BENZOFLEX 9-88SG” (available from Eastman ChemicalCompany). One type of the plasticizer may be used alone, or two or moretypes thereof may be used in combination at any ratio.

The ratio of the plasticizer in the first binder relative to 100 partsby weight of the polymer is preferably 1 part by weight or more, andmore preferably 5 parts by weight or more, and is preferably 35 parts byweight or less, and more preferably 30 parts by weight or less.

The refractive index of the first binder is usually 1.5 or more,preferably 1.52 or more, and more preferably 1.55 or more, and isusually 1.7 or less, preferably 1.65 or less, and more preferably 1.6 orless. When the refractive index of the first binder is equal to or morethan the lower limit of the above-described range, D1/L1 can be easilyadjusted within a suitable range using a small amount of the firstlight-scattering particles. Therefore, use of excessively large amountof the first light-scattering particles can be avoided. It is thus easyto smoothen the surface of the first light-scattering layer 120 and toincrease the adhesiveness of the first light-scattering layer 120. Whenthe refractive index is equal to or less than the upper limit, thechange in adhesiveness over time can be decreased, and the layer can bemade soft.

It is preferable that the first light-scattering layer 120 is formedonly of the first light-scattering particles and the first binder.Therefore, it is preferable that the amount of the first binder in thefirst light-scattering layer 120 is set so that the sum of the ratio ofthe first light-scattering particles and the ratio of the first binderis 100% by weight.

(1.2.4. Thickness of First Light-Scattering Layer 120)

The thickness D1 of the first light-scattering layer 120 is usually 5 μmor more, preferably 10 or more, and more preferably 15 μm or more, andis usually 50 μm or less, preferably 40 μm or less, and more preferably25 μm or less. When the thickness of the first light-scattering layer120 is equal to or more than the lower limit of the above-describedrange, light can be sufficiently scattered. When it is equal to or lessthan the upper limit, the surface of the first light-scattering layercan be made flat.

(1.2.5. Method for Producing First Light-Scattering Layer 120)

The first light-scattering layer 120 may be produced, for example, byapplying a coating liquid suitable for formation of the firstlight-scattering layer 120 onto a desired supporting surface, and ifnecessary, performing a curing treatment such as drying. In this case, aliquid composition containing the first light-scattering particles andthe first binder may be used as the coating liquid.

The coating liquid may contain an optional component, if necessary.Examples of the optional component may include an additive such as asilane coupling agent and a curing agent; and a solvent.

Examples of the silane coupling agent may include vinyltrimethoxysilane,vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,3-glycidoxypropylmethyldimethoxysilane,3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldimethoxysilane,3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane,3-methacryloxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane,3-methacryloxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane,N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane,3-triethylsilyl-N-(1,3-dimethyl-butylidene)propylamine,N-phenyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane,3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane,bis(triethoxysilylpropyl)tetrasulfide, and3-isocyanatepropyltriethoxysilane. Examples of the commerciallyavailable silane coupling agent may include a product with a trade nameof “KBM-803” (available from. Shin-Etsu Chemical Co., Ltd.). One type ofthe silane coupling agent may be used alone, or two or more typesthereof may be used in combination at any ratio.

The amount of the silane coupling agent relative to 100 parts by weightof the polymer in the first binder is preferably 0.05 part, by weight ormore, and more preferably 0.2 parts by weight or more, and is preferably5 parts by weight or less, and more preferably 3 parts by weight orless.

Examples of the curing agent may include an isocyanate compound.Specific examples of the curing agent may include an addition polymer ofisocyanate containing isophorone diisocyanate (for example, “NY-260A”available from Mitsubishi Chemical Corporation). One type of the curingagent may be used alone, or two or more types thereof may be used incombination at any ratio.

The amount of the curing agent relative to 100 parts by weight of thepolymer in the first binder is preferably 0.01 parts by weight or more,and more preferably 0.05 parts by weight or more, and is preferably 5parts by weight or less, and more preferably 1 part by weight or less.

Examples of the solvent may include the same examples as those of theorganic solvent used in production of the reactive modified metal oxideparticles. One type of the solvent may be used alone, or two or moretypes thereof may be used in combination at any ratio.

In production of each component to be contained in the coating liquid,the respective components may be obtained as a solution or a suspensioncontaining the respective components dissolved or dispersed in asolvent.

When each component to be contained in the coating liquid is acommercially available product, the respective components may beobtained in a form of solution or suspension. In such a case, thesolvent contained in the solution or suspension may be used as a part orall of the solvent of the coating liquid.

The amount of the solvent relative to 100 parts by weight of a totalsolid content of the coating liquid is preferably 50 parts weight ormore, and more preferably 100 parts by weight or more, and is preferably300 parts by weight or less, and more preferably 250 parts by weight orless. Herein, the solid content of the coating refers to a componentthat remains after drying of the coating liquid.

For example, the aforementioned coating liquid is applied onto a surface112D of the substrate film layer 112, and treated for curing, ifnecessary. In this manner, the first light-scattering layer 120 mayproduced. The first light-scattering layer 120 thus obtained may containthe components contained in the coating liquid. However, a part of thecomponents may be changed by a reaction or may be volatilized anddisappear. For example, by a drying step, reactive components such asthe silane coupling agent and the curing agent may be reacted to formanother substance, or the solvent may be volatilized and disappear.

[1.3. Substrate Plate Layer 130]

As the substrate plate layer 130, a transparent sheet is usually used.As an example of the material for the substrate plate layer, glass or atransparent resin may be used. Examples of the transparent resin usablefor the substrate plate layer 130 may include a thermoplastic resin, athermosetting resin, an ultraviolet curable resin, and an electron beamcurable resin. Among these, a thermoplastic resin is preferred in termsof easy processing. Examples of the thermoplastic resin may include apolyester resin, a polyacrylate resin, and a cycloolefin resin. One typethereof may be used alone, or two or more types thereof may be used incombination at any ratio.

The refractive index of the substrate plate layer 130 is preferablyclose to the refractive index of the first binder of the firstlight-scattering layer 120. Specifically, a difference between therefractive index of the substrate plate layer 130 and the refractiveindex of the first binder is preferably 0.15 or less, more preferably0.1 or less, and further preferably 0.05 or less.

In this manner, the light extraction efficiency of the organic ELlight-emitting device 100 can be enhanced.

When the substrate plate layer 130 is formed of a resin, the thicknessof the substrate plate layer 130 is preferably 20 μm to 300 μm. When thesubstrate plate layer 130 is formed of glass, the thickness of thesubstrate plate layer 130 is preferably 10 μm to 1,100 μm. The substrateplate layer 130 may or may not have flexibility. Therefore, for example,inflexible glass having a thickness of 700 μm may be employed as thesubstrate plate layer.

[1.4. Second. Light-Scattering Layer 140]

The second light-scattering layer 140 is a layer that can function as alight scattering structure for scattering light, and contains secondlight-scattering particles. The second light-scattering layer 140usually contains a second binder in order to hold the secondlight-scattering particles in the second light-scattering layer 140. Inthe second light-scattering layer 140, the second light-scatteringparticles are dispersed in the second binder.

The second binder is usually transparent. Light passing through thetransparent second binder is reflected on the interface between thesecond binder and the second light-scattering particles so as to bescattered.

When the second light-scattering layer 140 contains the secondlight-scattering particles, it is preferable that the secondlight-scattering layer 140 satisfies (D1/L1+D2/L2)<6. Herein, “D2”represents the thickness of the second light-scattering layer 140. “L2”represents the mean free path of light scattering in the secondlight-scattering layer 140. Specifically, a value of (D1/L1+D2/L2) ispreferably 0.5 or more, more preferably 0.8 or more, and particularlypreferably 1.4 or more, and is preferably 6 or less, and more preferably4.5 or less. Thereby the light extraction efficiency of the organic ELlight-emitting device 100 can be further enhanced.

As the second light-scattering particles, particles selected from theparticles described as the first light-scattering particles may beoptionally used. One type of the second light-scattering particles maybe used alone, or two or more types thereof may be used in combinationat any ratio.

The refractive index of the second light-scattering particles is usually1.2 or more, preferably 1.3 or more, and more preferably 1.4 or more,and is usually 1.6 or less, preferably 1.55 or less, and more preferably1.5 or less. When the refractive index of the second light-scatteringparticles is equal to or more than the lower limit of theabove-described range, variation of scattering property due tofluctuation of the particle diameter and the film thickness can besuppressed. When the refractive index is equal to or less than the upperlimit, light can be sufficiently scattered.

The average particle diameter of the second light-scattering particlesis preferably 0.2 or more, more preferably 0.3 μm or more, andparticularly preferably 0.4 μm or more, and is preferably 2 μm or less,more preferably 1 μm or less, and particularly preferably 0.9 μm orless. When the average particle diameter of the second light-scatteringparticles is equal to or more than the lower limit of theabove-described range, visible light can be stably scattered by thesecond light-scattering particles. When the average particle diameter isequal to or less than the upper limit, visible light can be efficientlyscattered by the second light-scattering particles. Further, the layerseach contained in the light-emitting element layer 150 are required tohave flatness. Therefore, it is preferable that the average particlediameter of the second light-scattering particles contained in thesecond light-scattering layer 140 disposed in the vicinity of thelight-emitting element layer 150 is small as described above.

The ratio of the second light-scattering particles in the secondlight-scattering layer 140 is preferably 0.5% by weight or more, andmore preferably 1% by weight or more, and is preferably 40% by weight orless, and more preferably 20% by weight or less. When the ratio of thesecond light-scattering particles falls within the above-describedrange, a desired light-scattering effect can be obtained to suppresscolor unevenness depending on a polar angle direction on thelight-emitting surface 100U.

As the second binder, a resin is usually used. When an adhesive havingadhesiveness is used as the resin, for example, a resin selected from arange of the adhesive described as the first binder may be optionallyused.

When the second binder has no adhesiveness, as the resin that can beused as the second binder, for example, a thermoplastic resin, athermosetting resin, or an energy ray curable resin such as aultraviolet curable resin and an electron beam curable resin may beused. In particular, a thermosetting resin and an energy ray curableresin are preferred from the viewpoints of high hardness and productionefficiency. Examples of the thermoplastic resin may include a polyesterresin, a polyacrylate resin, and a cycloolefin resin. Examples of theultraviolet curable resin may include an epoxy resin, an acrylic resin,a urethane resin, an ene/thiol resin, and an isocyanate resin. For theresins, a resin having a plurality of polymerizable functional groups ispreferred. One type thereof may be used alone, or two or more typesthereof may be used in combination at any ratio.

The refractive index of the second binder is usually 1.52 or more,preferably 1.55 or more, and more preferably 1.65 or more, and isusually 1.9 or less, preferably 1.85 or less, and more preferably 1.8 orless. When the refractive index of the second binder is equal to or morethan the lower limit of the above-described range, D2/L2 can be easilyadjusted within a suitable range even if a small amount of the secondlight-scattering particles are used. Therefore, use of excessively largeamount of the second light-scattering particles can be avoided.

Accordingly, the surface of the second light-scattering layer 140 can beeasily made smooth. When it is equal to or less than the upper limit, adifference in refractive index between the light-emitting element layer150 and the second binder can be decreased to suppress reflection.Further, particles during mixing the high refractive index nanoparticlescan be easily dispersed.

It is preferable that the second light-scattering layer 140 is formedonly of the second light-scattering particles and the second binder.Therefore, it is preferable that the amount of the second binder in thesecond light-scattering layer 140 is set so that the sum of the ratio ofthe second light-scattering particles and the ratio of the second binderis 100% by weight.

The thickness D2 of the second light-scattering layer 140 is usually 1μm or more, preferably 2 μm or more, and more preferably 3 μm or more,and is usually 30 μm or less, preferably 20 μm or less, and morepreferably 10 μm or less. When the thickness of the second lightscattering layer 140 is equal to or more than the lower limit of theabove-described range, the second light-scattering layer 140 cansufficiently scatter light. When it is equal to or less than the upperlimit, the surface during formation of a film can be made uniform andeven.

The second light-scattering layer 140 may be produced, for example, byapplying a coating liquid suitable for formation of the secondlight-scattering layer onto a desired supporting surface, and ifnecessary, performing a curing treatment such as drying.

As the coating liquid, a liquid composition containing the secondlight-scattering particles and the second binder may be used. Thecoating liquid may further contain a solvent, if necessary. Examples ofthe solvent may include the same examples as those of the organicsolvent used in production of the reactive modified metal oxideparticles. One type of the solvent may be used alone, or two or moretypes thereof may be used in combination at any ratio. The ratio of thesolvent in the coating liquid may be 10% by weight to 80% by weight.

The second light-scattering layer 140 may be produced by, for example,applying the aforementioned coating liquid onto a surface 130D of thesubstrate plate layer 130, and subjecting it to a curing treatment, ifnecessary. The second light-scattering layer 140 thus obtained maycontain the components contained in the coating liquid. However, a partof the components may be changed by a reaction or may be volatilized anddisappear.

[1.5. Light-Emitting Element. Layer 150]

The light-emitting element layer 150 usually includes two or moreelectrode layers and a light-emitting layer that is provided between theelectrode layers and can generate light by application of a voltagethereto from the electrode layers. Such a light-emitting element layermay be formed by sequentially forming layers such as the electrodelayers and the light-emitting layer on a substrate plate by a knownmethod such as sputtering. In this embodiment, the light-emittingelement layer 150 including the transparent electrode layer 151, thelight-emitting layer 152, and the reflecting electrode layer 153 in thisorder will be described as an example.

A light-emitting material for the light-emitting layer 152 is notparticularly limited, and a known material may be appropriatelyselected. As the light-emitting material for the light-emitting layer142, one type thereof may be used alone, or two or more types thereofmay be used in combination at any ratio. The light-emitting layer 152may be a layer having a single-layer structure including only one layer.Further, the light-emitting layer 152 may be a layer having a multilayerstructure including a plurality of layers in combination for adaptationto use as a light source. With such a structure, the light-emittinglayer 152 may be a layer that generates white light or light of colorclose to white.

As the material for the electrode layers, one type thereof may be usedalone, or two or more types thereof may be used in combination at anyratio. The electrode layers each may be a layer having a single-layerstructure including only one layer, or a layer having a multilayerstructure including two or more layers.

The light-emitting element layer 150 may further include, between thetransparent electrode layer 151 and the reflecting electrode layer 153,an optional layer (not shown), such as a hole injection layer, a holetransport layer, an electron transport layer, and an electron injectionlayer in addition to the light-emitting layer 152. Furthermore, thelight-emitting element layer 150 may include an optional component suchas a wiring for applying electricity to the transparent electrode layer151 and the reflecting electrode layer 153, and a peripheral structurefor sealing the light-emitting layer 152.

The material constituting a layer that may be contained in thelight-emitting element layer 150 is not particularly limited. Specificexamples thereof may include the following.

Examples of a material for the transparent electrode layer may includeindium tin oxide (ITO).

Examples of a material for the reflecting electrode layer may includealuminum and silver.

Examples of a material for a hole injection layer may include astarburst aromatic diamine compound.

Examples of a material for a hole transport layer may include atriphenyldiamine derivative.

Examples of a host material for a yellow light-emitting layer mayinclude a triphenyldiamine derivative. Examples of a dopant material forthe yellow light-emitting layer may include a tetracene derivative.

Examples of a material for green light-emitting layer may include apirazoline derivative.

Examples of a host material for a blue light-emitting layer may includean anthracene derivative. Examples of a dopant material for the bluelight-emitting layer may include a perylene derivative.

Examples of a material for a red light-emitting layer may include aeuropium complex.

Examples of a material for an electron transport layer may include analuminum quinoline complex (Alq).

The light-emitting layer 152 may be a combination of a plurality oflayers for constituting a light-emitting layer that generates light ofcolors in complementary relationship. Such a light-emitting layer iscalled a lamination type or a tandem type. A combination ofcomplementary colors relation may be, for example, yellow/blue,green/blue/red, or the like.

[1.6. Sealing Layer 160]

The sealing layer 160 is a layer for blocking water. It is preferablethat the sealing layer 160 has a function of blocking not only water butalso oxygen. In this manner, the organic material in the light-emittingelement layer 150 can be prevented from deteriorating due to water vaporand oxygen. The sealing layer 160 may be formed, for example, of anorganic material such as a resin or an inorganic material such as metaland a metal compound. Such a sealing layer 160 may be formed, forexample, by bonding a sealing film formed of an appropriate material orthe like to the surface of the light-emitting element layer 150.

[1.7. Main Advantages of Organic EL Light-Emitting Device 100]

In the organic EL light-emitting device 100 having the aforementionedconfiguration, when a voltage is applied by the transparent electrodelayer 151 and the reflecting electrode layer 153, the light-emittinglayer 152 generates light. The light thus generated passes through thetransparent electrode layer 151 or is reflected by the reflectingelectrode layer 153 and then passes through the light-emitting layer 152and the transparent electrode layer 151. Subsequently, the light passesthrough the second light-scattering layer 140, the substrate plate layer130, the first light-scattering layer 120, the substrate film layer 112,and the concavo-convex structure layer 111, and exits through thelight-emitting surface 100U. In this case, when the aforementioned lightpasses through the first light-scattering layer 120, it is scattered dueto reflection on the surface of the first light-scattering particlescontained in the first light-scattering layer 120. Further, when theaforementioned light passes through the second light-scattering layer150, it is scattered due to reflection on the surface of the secondlight-scattering particles contained in the second light-scatteringlayer 140. Since prisms 171 are provided on the light-emitting surface100U, the aforementioned light easily enters the light-emitting surface100U at an incident angle at which the light can pass through thelight-emitting surface 100U.

In addition to these matters, the organic EL light-emitting device 100according to this embodiment satisfies the aforementioned requirements(A) and (B). In this manner, light generated in the light-emitting layer152 easily exits through the light-emitting surface 100U to the outside.Accordingly, the organic EL light-emitting device 100 according to thisembodiment can have high light extraction efficiency.

The light extraction efficiency may be evaluated on the basis of a lightextraction efficiency Q that is obtained by comparison of the organic ELlight-emitting device 100 according to this embodiment with a controllight-emitting device. Herein, the light extraction efficiency Q isobtained by equation: “Q=(total light flux from the organic ELlight-emitting device 100 according to this embodiment)/(total lightflux from the control light-emitting device)”. As the controllight-emitting device, a light-emitting device that is differentiatedfrom the organic EL light-emitting device 100 according to thisembodiment only on the point of the presence or absence of a part of thelayers may be used. For example, a light-emitting device having the samestructure as that of the organic EL light-emitting device 100 exceptthat the layers from the light-emitting surface structure layer 110 tothe second light-scattering layer 140 are not provided may be used asthe control light-emitting device. Alternatively, a light-emittingdevice additionally having another difference in configuration that doesnot largely affect the light extraction efficiency may also be used.

With the organic EL light-emitting device 100, color unevenness mayusually be reduced. Herein, the color unevenness represents a phenomenonin which the color of light observed is different depending on anobservation direction during observation of the light-emitting surface100U.

2. Second Embodiment

In the aforementioned first embodiment, the second light-scatteringlayer containing the second light-scattering particles and the secondbinder has been described as an example of a light-scattering structure.However, the light-scattering structure is not limited to such alight-scattering layer, and any structure capable of scattering lightgenerated in the light-emitting layer may be used. Hereinafter, anexample of organic EL light-emitting device having a light-scatteringstructure other than the second light-scattering layer containing thesecond light-scattering particles and the second binder will bedescribed with reference to the drawings.

FIG. 4 is a perspective view schematically showing an organic ELlight-emitting device 200 according to a second embodiment of thepresent invention. In the organic EL light-emitting device 200 shown inFIG. 4, the same portions as those in the organic EL light-emittingdevice 100 according to the first embodiment are denoted by the samenumerals used in the description of the first embodiment.

As shown in FIG. 4, the organic EL light-emitting device 200 accordingto the second embodiment of the present invention has the sameconfiguration as that of the organic EL light-emitting device 100according to the first embodiment except that a light-scatteringstructure layer 240 is provided in place of the second light-scatteringlayer 140.

The light-scattering structure layer 240 has a first light-transmittinglayer 241 and a second light-transmitting layer 242 that are differentfrom each other in the refractive indices. The first light-transmittinglayer 241 and the second light-transmitting layer 242 are in contactwith each other at an interface 243. The first light-transmitting layer241 and the second light-transmitting layer 242 are formed to havenon-uniform thicknesses. Therefore, the interface 243 is a non-flatconcavo-convex surface, and includes a plurality of surface portions243A, 243B, and 243C that are not parallel to one another.

When light passes through the aforementioned interface 243, the light isusually refracted depending on an incident angle to the interface 243.Herein, the interface 243 includes the plural surface portions 243A to243C that are not parallel to one another as described above. Therefore,light passing through the interface 243 is refracted at each of thesurface portions 243A to 243C. Accordingly, the light passing throughthe interface 243 travels in a plurality of different directions.

Consequently, light can be scattered by the light-scattering structurelayer 240.

The organic EL light-emitting device 200 having the light-scatteringstructure layer 240 in place of the second light-scattering layer 140may be used in the same manner as the organic EL light-emitting device100 according to the first embodiment, and the same advantages as thoseof the organic EL light-emitting device 100 according to the firstembodiment can be obtained.

3. Modifications

The present invention is not restricted to the embodiments describedabove, and may be implemented with further modifications.

For example, the concave portions and the convex portions such as prismscontained in the concavo-convex structures are not limited to thoseextending linearly in one direction. FIG. 5 is a plan view schematicallyshowing a light-emitting, surface 300U of a concavo-convex structurelayer 311 according to an example. As shown in FIG. 5, a concavo-convexstructure 370 in a streak array pattern may be provided, for example, asa group of prisms 371 each of which extends in a curved manner in aplurality of different directions.

For example, unlike the aforementioned embodiments, the depth of theconcave portions and the height of the convex portions in theconcavo-convex structure in a streak array pattern may not be constantand may be different.

In the aforementioned embodiments, explanation has been made referringto examples wherein each of the prisms 171 is continuously provided overthe entire light-emitting surface 100U in the extending direction of theprisms 171. However, the concave portions and the convex portions likethe prisms 171 may not be necessarily provided continuously over theentire light-emitting surface 100U in the extending direction of theconcave portions and the convex portions. For example, spacing forseparating the respective prisms 171 into a plurality of prisms in theextending direction of the prisms 171 (depth direction in FIG. 1) may beprovided on the concavo-convex structure layer 111 of the organic ELlight-emitting device 100 according to the first embodiment as shown inFIG. 1.

For example, even when the reflecting electrode layer 153 of theabove-described embodiments is replaced by a multilayer member includinga transparent electrode layer and a reflective layer in combination, adevice providing the same effects as those of the organic ELlight-emitting device according to the above-described embodiments maybe obtained.

For example, the reflecting electrode layer 153 of the above-describedembodiments may be replaced by a transparent electrode layer. By suchreplacement, an organic EL light-emitting device capable of emittinglight from both surfaces may be obtained.

Furthermore, the organic EL light-emitting device may not necessarilyinclude the substrate film layer 112, the substrate plate layer 130, andthe sealing layer 160. The organic EL light-emitting device may furtherinclude an optional layer in addition to the aforementioned layers.

4. Application of Organic EL Light-Emitting Device

The organic EL light-emitting device of the present invention may beused, for example, for applications such as a lighting apparatus and abacklight device. A lighting apparatus has the organic EL light-emittingdevice of the present invention as a light source, and may includeoptional components such as a member holding the light source and acircuit for supplying power. A backlight device has the organic ELlight-emitting device of the present invention as a light source, andmay include optional components such as a housing, a circuit forsupplying power, a diffusion plate for making emitted light uniform, adiffusion sheet, and a prism sheet. The backlight device may be used asa backlight of a display device of controlling pixels to display animage such as a liquid crystal display device, and a display device ofdisplaying a fixed image such as a sign board.

EXAMPLES

Hereinafter, the present invention will be specifically described byshowing Examples. However, the present invention is not limited to thefollowing Examples. The present invention may be freely modified forimplementation without departing from the scope of claims of the presentinvention and equivalents thereto.

Unless otherwise specified, “%” and “part” that represent amounts ofmaterials in the following Examples and Comparative Examples are basedon weight. Unless otherwise specified, operations in Examples andComparative Examples were performed under environment of normaltemperature and normal pressure.

In the following Examples and Comparative Examples, the mean free pathof light scattering in a light-scattering layer was calculated withrespect to light having a wavelength of 550 nm in vacuum by theaforementioned method in accordance with the Mie scattering theory.

[I. Examples and Comparative Examples based on Actual Measuring]

Example 1

(1-1. Preparation of Ultraviolet Curable Resin Composition A)

A plastic container was charged with 44 parts by weight of a slurrycontaining reactive modified zirconia oxide as high refractive indexnanoparticles (“ZR-010” available from SOLAR CO., Ltd., solvent: methylethyl ketone, particle content: 30%, particle specific gravity: about 4,volume average particle diameter of particles of reactive modifiedzirconia oxide: 15 nm, refractive index: about 1.9), 33 parts by weightof methyl ethyl ketone as a solvent, 1.3 parts by weight of siliconeparticles as second light-scattering particles (volume average particlediameter: 0.5 μm, specific gravity: 1.32, refractive index: 1.43), and500 parts by weight of zirconia balls for dispersion. (“YTZ-0.5”available from NIKKATO CORPORATION).

This container was disposed on a ball mill rack, and ball milldispersion was performed at a rate of 2 rotations per second for 1 hour.After the ball mill dispersion, the content of the container was sievedto remove the zirconia balls, thereby obtaining a mixture 1.

To the mixture 1, 8.7 parts by weight of an ultraviolet curable resin(“P5790PS3A” available from Daido Chemical Corporation., specificgravity: 1.1) was added, and the mixture was stirred for 15 minutes toobtain an ultraviolet curable resin composition A.

(1-2. Measurement of Refractive Index of Binder (Second Binder) ofSecond Light-Scattering Layer)

An ultraviolet curable resin composition A′ containing no siliconeparticles was obtained by the same operation as in the aforementionedstep (1-1) except that silicone particles were not added.

The curable resin composition A′ was applied onto a surface of a glassplate by a bar coater so that the thickness after drying was 10 μm, andcured by irradiation with ultraviolet rays of 500 mJ. The refractiveindex of the layer of the cured resin composition A′ was measured by anellipsometer (M-2000″ manufactured by J. A. Woollam. Japan) and wasfound to be 1.63.

(1-3. Production of Organic EL Element)

The aforementioned ultraviolet curable resin composition A was appliedby spin coating onto a surface of a glass substrate plate having athickness of 0.7 mm and a refractive index of 1.52, and the thicknesswas adjusted Sc) that the thickness of the final film was 3 μm.Subsequently, the glass substrate plate was placed on a hot plate at 80°C. so as to dry the layer of the resin composition A for 5 minutes.Then, the layer was cured by irradiation with ultraviolet rays of 500mJ. In this manner, a second light-scattering layer was formed on theglass substrate plate.

On the obtained second light-scattering layer, further a transparentelectrode layer having a thickness of 100 nm, a hole transport layerhaving a thickness of 10 nm, a yellow light-emitting layer having athickness of 20 nm, a blue light-emitting layer having a thickness of 15nm, an electron transport layer having a thickness of 15 nm, an electroninjection layer having a thickness of 1 nm, and a reflecting electrodelayer having a thickness of 100 nm were formed in this order. All of thelayers from the hole transporting layer to the electron transport layerwere formed of organic materials. The yellow light-emitting layer andthe blue light-emitting layer had emission spectra that are differentfrom each other.

Materials forming each layer from the transparent electrode layer to thereflecting electrode layer were as follows.

-   Transparent electrode layer: tin-doped indium oxide (ITO)-   Hole transport layer: 4,4′-bis[N-(naphthyl)-N-phenylamino]biphenyl    (α-NPD)-   Yellow light-emitting layer: 1.5% by weight rubrene-doped α-NPD-   Blue light-emitting layer: 10% by weight iridium complex-doped    4,4′-dicarbazolyl-1,1′-biphenyl (CBP)-   Electron transport layer: phenanthroline derivative (BCP)-   Electron injection layer: lithium fluoride (LiF)-   Reflecting electrode layer: Al

The transparent electrode layer was formed by a reactive sputteringmethod using an ITO target.

The layers from the hole injection layer to the reflecting electrodelayer were formed by disposing in a vacuum vapor deposition device aglass substrate plate having the transparent electrode layer formedthereon, and then sequentially vapor-depositing the materials for thelayers from the hole transport layer to the reflecting electrode layerby a resistance heating. The vapor deposition was performed at a systeminternal pressure of 5×10⁻³ Pa and an evaporation rate of 0.1 nm/s to0.2 nm/s.

Subsequently, a wiring for applying electricity was attached to theelectrode layer, and the layers from the hole transport layer to thereflecting electrode layer were sealed with a sealing substrate plate.Thus, a light-emitting element having a layer structure of (glasssubstrate plate)/(second-light-scattering layer)/(transparent electrodelayer)/(hole transport layer)/(yellow light-emitting layer)/(bluelight-emitting layer)/(electron transport layer)/(electron injectionlayer)/(reflecting electrode layer)/(sealing substrate plate) wasproduced.

(1-4. Preparation of Adhesive Composition B)

A plastic container was charged with 85 parts by weight of a slurrycontaining reactive modified zirconia oxide as high refractive indexnanoparticles (“ZR-010” available from SOLAR CO., Ltd., solvent: methylethyl ketone, particle content: 30%, particle specific gravity: about 4,volume average particle diameter of particles of reactive modifiedzirconia oxide: 15 nm, refractive index: about 1.9), 5 parts by weightof silicone particles as first light-scattering particles (“XC-99”available from Momentive Performance Materials Inc., volume averageparticle diameter: 0.7 μm, specific gravity: 1.32, refractive index:1.43), and 500 parts by weight of zirconia balls for dispersion.(“YTZ-0.5” available from NIKKATO CORPORATION).

This container was disposed on a bail mill rack, and ball milldispersion was performed at a rate of 2 rotations per second for 30minutes. After the ball mill dispersion, the content of the containerwas sieved to remove the zirconia balls, thereby obtaining a mixture 2.

To the mixture 2, 100 parts by weight of an acrylic adhesive(“X-311033S” available from SAIDEN CHEMICAL INDUSTRY CO., LTD., solidcontent: 35%, specific gravity: 1.1) and 5 parts by weight of aplasticizer (“BENZOFLEX 9-88SG” available from. Eastman ChemicalCompany, diethylene glycol dibenzoate, specific gravity: about 1.0) wereadded, and the mixture was stirred for 15 minutes. Subsequently, 1 partby weight of a silane coupling agent (“KBM-803” available from.Shin-Etsu Chemical Co., Ltd., 3-mercaptopropyltrimethoxysilane) and 0.6parts by weight of a curing agent (“NY-260A” available from MitsubishiChemical Corporation) were added, and the mixture was stirred for 15minutes to obtain an adhesive composition B for forming a firstlight-scattering layer.

(1-5. Measurement of Refractive Index of Binder (First Binder) of FirstLight-Scattering Layer)

An adhesive composition B′ containing no silicone particles was obtainedby the same operation as in the above-described step (1-4) except thatsilicone particles were riot added.

The adhesive composition B′ was applied onto a surface of a glass plateso that the thickness after drying was 10 μm, and dried at 80° C. for 5minutes to form a test adhesive layer. The refractive index of the testadhesive layer was measured by an ellipsometer (“M-2000” manufactured byJ. A. Woollam Japan) and found to be 1.56.

(1-6. Preparation of Scattering Adhesive Sheet)

The adhesive composition B obtained above was applied onto a surface ora substrate film layer having a thickness of 100 μm (“ZEONOR filmZF14-100” available from ZEON Corporation, refractive index: 1.52) sothat the thickness after drying was 35 μm, and dried at 80° C. for 5minutes. Thus, a first light-scattering layer (light-scattering adhesivelayer) having adhesiveness was formed on the substrate film layer, toobtain a scattering adhesive sheet having the substrate film layer andthe first light-scattering layer.

(1-7. Formation of Concavo-Convex Structure Layer)

Onto a surface of the scattering adhesive sheet opposite to the firstlight-scattering layer, a UV curable resin (“P5790PS3C” available fromDaido Chemical Corporation.) was applied so as to have a thickness of 10μm. On a film of the applied UV curable resin, a metal mold wasdisposed. On the surface of this metal mold, a concavo-convex structurein a streak array pattern in which prisms each having a cross section ofisosceles triangle with an apex angle of 60° at pitches of 10 μm wereuniformly disposed. The metal mold was pressed onto the film of the UVcurable resin, and the film of the UV curable resin was irradiated withultraviolet rays of 500 mJ through the first light-scattering layer. Asa result, the film of the UV curable resin was cured to form aconcavo-convex structure layer on a side of the substrate film layeropposite to the first light-scattering layer.

(1-8. Production of Organic EL Light-Emitting Device)

The scattering adhesive sheet having the concavo-convex structure layerwas bonded to a surface of the light-emitting element obtained in theabove-described step (1-3) on a side of the glass substrate plate. Thus,an organic EL light-emitting device having a layer structure of(concavo-convex structure layer)/(substrate film layer)/(firstlight-scattering layer formed of adhesive composition B)/(glasssubstrate plate)/(second light-scattering layer)/(transparent electrodelayer)/(hole transport layer)/(yellow light-emitting layer)/(bluelight-emitting layer)/(electron transport layer)/(electron injectionlayer)/(reflecting electrode layer)/(sealing substrate plate) wasobtained.

Example 2 (2-1. Preparation of Adhesive Composition C)

A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, athermometer, and a stirrer alas prepared. 233 parts of ethyl acetate asa solvent; 30 parts of butyl acrylate, 70 parts of phenoxyethylacrylate, 0.5 parts of acrylic acid, 0.3 parts of 4-hydroxybutylacrylate, and 0.2 parts of 2,2′-azobisisobutyronitrile were placed inthis reaction vessel. After nitrogen purging, the temperature in thereaction vessel was increased to 55° C., and a polymerization reactionwas conducted for 15 hours to obtain a solution of an acrylic copolymerhaving a weight average molecular weight of 810,000. The refractiveindex of the acrylic copolymer was 1.53.

To this solution, 60 parts of a copolymer of α-methylstyrene withstyrene (“Kristalex 3085” available from Eastman Chemical Company,softening point: 82° C. to 88° C., weight average molecular weight:1,200, refractive index: 1.61) and 7 parts of a styrene oligomer(“Piccolastic A5” available from Eastman Chemical Company, softeningpoint: equal to or lower than room temperature, weight: averagemolecular weight: 430, refractive index: 1.60) as tackifiers(adhesiveness imparting agents); 0.6 parts of an isophorone diisocyanateadduct of trimethylol propane as a crosslinker; and 20 parts by weightof silicone particles (“XC-99” available from Momentive PerformanceMaterials Inc., volume average particle diameter: 0.7 μm, specificgravity: 1.32) as first light-scattering particles were added relativeto 100 parts of solid content of the aforementioned acrylic copolymer,thereby obtaining an adhesive composition C.

(2-2. Measurement of Refractive Index of Binder of FirstLight-Scattering Layer)

An adhesive composition C′ containing no silicone particles was obtainedby the same operation as in the above-described step (2-1) except thatsilicone particles were not added.

The adhesive composition Cr was applied onto a surface of a glass plateso that the thickness after crying was 10 μm, and dried at 80° C. for 5minutes to form a test adhesive layer. The refractive index of the testadhesive layer was measured by an ellipsometer (“M-2000” manufactured byJ. A. Woollam Japan) and was found to be 1.56.

(2-3. Production of Organic EL Light-Emitting Device)

An organic EL light-emitting device having a layer structure of(concavo-convex structure layer)/(substrate film layer)/(firstlight-scattering layer formed of adhesive composition C)/(glasssubstrate plate)/(second light-scattering layer)/(transparent electrodelayer)/(hole transport layer)/(yellow light-emitting layer)/(bluelight-emitting layer)/(electron transport layer)/(electron injectionlayer)/(reflecting electrode layer)/(sealing substrate plate) wasobtained in the same manner as in Example 1 except that the adhesivecomposition C was used in place of the adhesive composition B in theabove-described step (1-6).

Comparative Example 1

An organic EL light-emitting device having a layer structure of(substrate film layer)/(first light-scattering layer formed of adhesivecomposition B)/(glass substrate plate)/(second light-scatteringlayer)/(transparent electrode layer)/(hole transport layer)/(yellowlight-emitting layer)/(blue light-emitting layer)/(electron transportlayer)/(electron injection layer)/(reflecting electrode layer)/(sealingsubstrate plate) was obtained in the same manner as in Example 1 exceptthat a step of forming a concavo-convex structure layer on a scatteringadhesive sheet (i.e., the step (1-7) of Example 1) was not performed.

Comparative Example 2

An organic EL light-emitting device having a layer structure of(substrate film layer)/(first light-scattering layer formed of adhesivecomposition C)/(glass substrate plate)/(second light-scatteringlayer)/(transparent electrode layer)/(hole transport layer)/(yellowlight-emitting layer)/(blue light-emitting layer)/(electron transportlayer)/(electron injection layer)/(reflecting electrode layer)/(sealingsubstrate plate) was obtained in the same manner as in Example 2 exceptthat a step of forming a concavo-convex structure layer on a scatteringadhesive sheet was not performed.

[Evaluation]

[Calculation of Mean Free PELL of Scattering in Light-Scattering Layer]

In Examples and Comparative Examples described above, the mean free pathL1 of light scattering in the first light-scattering layer wascalculated in accordance with the Mie scattering theory using athickness of the first light-scattering layer of 35 μm, a refractiveindex of the binder of 1.56, an average particle diameter of the firstlight-scattering particles of 0.7 μm, and a concentration of the firstlight-scattering particles relative to the solid content of the firstlight-scattering layer of 6.9% by weight. It was found that was 14 μm.

Furthermore, in Examples and Comparative Examples described above, themean free path L2 of light scattering in the second light-scatteringlayer was calculated using a thickness of the second light-scatteringlayer of 3 μm, a refractive index of the binder of 1.63, an averageparticle diameter of the second light-scattering particles of 0.5 μm,and a concentration of the second light-scattering particles relative tothe solid content of the second light-scattering layer of 5.6% byweight. It was found that L2 was 9 μm.

Therefore, in. Examples and Comparative Examples described above, D1/L1in the first light-scattering layer was 2.5, and D2/L2 in the secondlight-scattering layer was 0.33.

[Measurement of Total Light Flux]

The total light flux of the organic EL light-emitting devices producedin Examples and Comparative Example described above were measured by ahigh-speed goniophotometric measurement system (“IMAGING SPHERE”manufactured by Radiant Imaging, Inc.). The measured total light fluxwas divided by the total light flux of the light-emitting elementobtained in the step (1-3) of Example 1 to obtain a light extractionefficiency. The results are shown in the following Table 1.

TABLE 1 results of Examples 1, 2 and Comparative Examples 1, 2Comparative Comparative Example 1 Example 2 Example 1 Example 2 D1/L12.5 2.5 2.5 2.5 D2/L2 0.33 0.33 0.33 0.33 Concavo-convex Present PresentAbsent Absent structure layer Light extraction 1.2 1.2 1.12 1.12efficiency (times)

As seen from the Table 1, high light extraction. efficiency is obtainedin Examples 1 and 2. It is confirmed that the present invention canachieve an organic EL light-emitting device that has a concavo-convexstructure in a streak array pattern and is excellent in light extractionefficiency.

In the first light-scattering layer using a polymer having a highrefractive index as a binder as shown in Example 2, expensive highrefractive index nanoparticles such as zirconia oxide are not necessary.Further, a complex operation such as ball mill treatment for dispersionof high refractive index nanoparticles is not necessary. Therefore, ispreferable that a binder containing a polymer having a high refractiveindex is used.

[II. Examples on the basis of Simulation]

Example 3 Range of D1/L1]

For a model of organic EL light-emitting device, the total light fluxwas calculated by an optical simulation using a program (“Light Tools”manufactured by ORA).

Settings for the organic EL light-emitting device modeled wereconfigured so as to have a layer structure of (concavo-convex structurelayer)/(substrate film layer)/(first light-scattering layer)/(glasssubstrate plate)/(second light-scattering layer)/(transparent electrodelayer)/(light-emitting layer)/(reflecting electrode layer).

Settings for the concavo-convex structure layer were configured so as tohave a concavo-convex structure in which prisms each having a crosssection of isosceles triangle were uniformly disposed. As to theconcavo-convex structure layer, the pitch of the prisms was set to 20μm, the apex angle of the prisms was set to 60°, and the refractiveindex was set to 1.52.

Settings for the substrate film layer were configured so as to have arefractive index of 1.52 and a thickness of 100 μm.

Settings for the first light-scattering layer were configured so thatthe refractive index of the first light-scattering particles was 1.43,and the refractive index of the binder was 1.56.

Settings for the glass substrate ate were configured so as to have arefractive index of 1.52 and a thickness of 600 μm.

Settings for the second light-scattering layer were configured so thatthe average particle diameter of the second light-scattering particleswas 0.5 μm, the refractive index of the second light-scatteringparticles was 1.43, the volume concentration of the secondlight-scattering particles was 1%, the refractive index of the binderwas 1.75, and the thickness thereof was 5 μm. D2/L2 was 0.15.

Settings for the transparent electrode layer were configured so as tohave a refractive index of 1.8 and a thickness of 0.15

Settings for the light-emitting layer were configured so as to have arefractive index of 1.8 and a thickness of 0.2 μm.

Settings for the reflecting electrode layer were configured so as tohave a reflectance of 85%.

Further, on an interface between the transparent electrode layer and thesecond light-scattering layer, a virtual light-emitting surface ofLambertan distribution was set.

As to the organic EL light-emitting device modeled as described above,calculations for the total light flux were performed with variations ofD1/L1 that were generated by varying the thickness of the firstlight-scattering layer and the concentration of the firstlight-scattering particles in the first light-scattering layer.

The calculations for the total light flux were performed for cases wherethe average particle diameters φ of the first light-scattering particleswere set to 0.4 μm, 0.7 μm, 1.0 μm, and 2.0 μm, respectively. Theresults of calculated total light flux are shown as relative values inFIG. 6.

From FIG. 6, it is confirmed that higher light extraction efficiency isobtained in a range of D1/L1<15 when the average particle diameter ofthe first light-scattering particles falls within a range of 0.4 μm to 2μm. In particular, it is confirmed that the light extraction efficiencyis maximized in a range of D1/L1<6 when the average particle diameter ofthe first light-scattering particles falls within a range of 0.4 μm to 1μm.

Example 4 Range of (D1/L1-D2/L2)

For a model of organic EL light-emitting device, the total light fluxwas calculated by the optical simulation using the program. (“LightTools” manufactured by

Settings for the organic EL light-emitting device modeled wereconfigured so as to have a layer structure of (concavo-convex structurelayer)/(substrate film layer) (first light-scattering layer)/(glasssubstrate plate) (second light-scattering layer)/(transparent electrodelayer)/(light-emitting layer)/(reflecting electrode layer).

Settings for the concavo-convex structure layer were configured so as tohave a concavo-convex structure in which prisms each having a crosssection of isosceles triangle were uniformly disposed. As to theconcavo-convex structure layer, the pitch of the prisms was set to 20μm, the apex angle of the prisms was set to 60°, and the refractiveindex was set to 1.52.

Settings for the substrate film layer were configured so as to have arefractive index of 1.52 and a thickness of 100 μm.

Settings for the first light-scattering layer were configured so thatthe average particle diameter of the first light-scattering particleswas 0.7 μm, the refractive index of the first light-scattering particleswas 1.43, and the refractive index of the binder was 1.56.

Settings for the glass substrate plate were configured so as to have arefractive index of 1.52 and a thickness of 600 μm.

Settings for the second light-scattering layer were configured so thatthe average particle diameter of the second light-scattering particleswas 0.5 μm, the refractive index of the second light-scatteringparticles was 1.43, and the refractive index of the binder was 1.75.

Settings for the transparent electrode layer were configured so as tohave a refractive index of 1.8 and a thickness of 0.15 μm.

Settings for the light-emitting layer were configured so as to have arefractive index of 1.8 and a thickness of 0.2 μm.

Settings for the reflecting electrode layer were configured so as tohave a reflectance of 85%.

Further, on an interface between the transparent electrode layer and thesecond light-scattering layer, a virtual light-emitting surface ofLambertian distribution was set.

As to the organic EL light-emitting device modeled as described above,calculations for the total light flux were performed. The calculationsfor the total light flux were performed with variations of D1/L1 andD2/L2 as shown in Table 2 that were generated by varying the thicknessof the first light-scattering layer, the concentration of the firstlight-scattering particles in the first light-scattering layer, thethickness of the second light-scattering layer, and the concentration ofthe second light-scattering particles in the second light-scatteringlayer. The results of calculated total light flux are shown as relativevalues in Table 2 and FIG. 7.

TABLE 2 [total light flux calculated by simulation according to Example3 (relative value)] D2/L2 0.15 0.4 0.8 1.5 3 4.5 7.7 D1/L1 0 0.594 0.6640.708 0.734 0.739 0.733 0.714 0.4 0.655 0.693 0.720 0.736 0.738 0.7320.713 1.5 0.686 0.713 0.728 0.737 0.736 0.727 0.709 2.5 0.692 0.7170.728 0.735 0.732 0.723 0.705 4.5 0.689 0.712 0.723 0.729 0.726 0.7150.696 7.7 0.678 0.700 0.709 0.713 0.708 0.715 0.682

As seen from Table 2, when both the values of D1/L1 and D2/L2 are large,the total light flux starts to decrease. Accordingly, (D1/L1+D2/L2)<6 isappropriate.

Example 5 Apex Angle of Prism

For a model of an organic EL light-emitting device, the total light fluxwas calculated by the optical simulation using the program (“LightTools” manufactured by ORA).

Settings for the organic Em light-emitting device modeled wereconfigured so as to have a layer structure of (concavo-convex structurelayer)/(substrate film layer)/(first light-scattering layer)/(glasssubstrate plate)/(second light-scattering layer)/(transparent electrodelayer)/(light-emitting layer)/(reflecting electrode layer).

Settings for the concavo-convex structure layer were configured so as tohave a concavo-convex structure in which prisms each having a crosssection of isosceles triangle were uniformly disposed. As to theconcavo-convex structure layer, the pitch of the prisms was set to 20μm, and the refractive index was set to 1.52.

Settings for the substrate film layer were configured so as to have arefractive index of 1.52 and a thickness of 100 μm.

Settings for the first light-scattering layer were configured so thatthe average particle diameter of the first light-scattering particleswas 0.7 μm, the refractive index of the first light-scattering particleswas 1.43, the volume concentration of the first light-scatteringparticles was 8%, the refractive index of the binder was 1.56, and thethickness was 20 μm. D1/L1 was 1.5.

Settings for the glass substrate plate were configured so as to have arefractive index of 1.52 and a thickness of 600 μm.

Settings for the second light-scattering layer were configured so thatthe average particle diameter of the second light-scattering particleswas 0.5 μm, the refractive index of the second light-scatteringparticles was 1.43, and the refractive index of the binder was 1.75.

Settings for the transparent electrode layer were configured so as tohave a refractive index of 1.8 and a thickness of 0.15 μm.

Settings for the light-emitting layer were configured so as to have arefractive index of 1.8 and a thickness of 0.2 μm.

Settings for the reflecting electrode layer were configured so as tohave a reflectance of 85%.

Further, on an interface between the transparent electrode layer and thesecond light-scattering layer, a virtual light-emitting surface ofLambertian distribution was set.

As to the organic EL light-emitting device modeled as described above,calculations for the total light flux were performed with variations ofthe apex angle of the prisms of the concavo-convex structure layer. Thecalculations for the total light flux were performed with each ofvariations in which D2/L2 was set to 0.4, 0.8, 1.5, and 3 by varying thethickness of the second light-scattering layer and the concentration ofthe second light-scattering particles in the second light-scatteringlayer. The results of calculated total light flux are shown as relativevalues in FIG. 8.

As seen from FIG. 8, in a case where D2/L2 is as small as about 0.4 toabout 0.8, the total light flux is maximized when the apex angle of theprisms of the concavo-convex structure layer is about 60° to about 70°.FIG. 8 also shows that, in a case where D2/L2 is large, an acute apexangle of the prisms brings about enhancement of the total light flux.Therefore, when the apex angle of prisms of the concavo-convex structurelayer is about 80° or smaller, the light extraction efficiency can bemade particularly large.

[Reference Example 1]

FIG. 9 shows ratios D/L or a thickness D of a layer containinglight-scattering particles and a binder relative to a mean free path Lof light scattering in cases of using either one of binders having arefractive index of 1.48 or 1.56. In these cases, the thickness of thelayer was 20 μm, the average particle diameter of light-scatteringparticles was 0.7 μm, and the refractive index of the light-scatteringparticles was 1.43. The specific gravity of the binder was 1, and thespecific gravity of the light-scattering particles was 1.32.

As seen from FIG. 9, when a binder having a higher refractive index isused, a larger value of D/L can be obtained using a small amount of thelight-scattering particles. Therefore, this shows that when a binderhaving higher refractive index is used, desired D/L is easily obtainedand as a result, the light extraction efficiency is easily improved.

DESCRIPTION OF NUMERALS:

100 organic EL light-emitting device

100U light-emitting surface

110 light-emitting surface structure layer

111 concavo-convex structure layer

112 substrate film layer

112D surface of substrate film layer

120 first light-scattering layer

130 substrate plate layer

130D surface of substrate plate layer

140 second light-scattering layer

150 light-emitting element layer

151 transparent electrode layer

152 light-emitting layer

153 reflecting electrode layer

160 sealing layer

170 concavo-convex structure

171 prism

200 organic EL light-emitting device

241 first light-transmitting layer

242 second light-transmitting layer

243 interface

243A-243C surface portions

300U light-emitting surface

311 concavo-convex structure layer

370 concavo-convex structure

371 prism

1. An organic EL light-emitting device comprising: a light-emittinglayer capable of generating light; a light-scattering structure capableof scattering the light; a first light-scattering layer containing firstlight-scattering particles having an average particle diameter of 0.1 μmto 2 μm and a first binder; and a concavo-convex structure in a streakarray pattern, the light emitting layer, the light-scattering structure,the first light-scattering layer, and the concavo-convex structure beingdisposed in this order, wherein a mean free path L1 of light scatteringin the first light-scattering layer and a thickness D1 of the firstlight-scattering layer satisfy D1/L1<15.
 2. The organic ELlight-emitting device according to claim 1, wherein the average particlediameter of the first light-scattering particles is 0.4 μm to 1 μm, andD1/L1<6.
 3. The organic EL light-emitting device according to claim 1,wherein the light-scattering structure is a second light-scatteringlayer containing second light-scattering particles, and a mean free pathL2 of light scattering in the second light-scattering layer and athickness D2 of the second light-scattering layer satisfy(D1/L1+D2/L2)<6.
 4. The organic EL light-emitting device according toclaim 3, wherein a ratio of the second light-scattering particles in thesecond light-scattering layer is 0.5% by weight or more and 40% byweight or less.
 5. The organic EL light-emitting device according toclaim 3, wherein an average particle diameter of the secondlight-scattering particles is 0.2 μm or more and 2 μm or less.
 6. Theorganic EL light-emitting device according to claim 1, wherein theconcavo-convex structure includes a prism.
 7. The organic ELlight-emitting device according to claim 6, wherein the prism has anapex angle of 80° or smaller.
 8. The organic EL light-emitting deviceaccording to claim 1, wherein the first binder has a refractive index of1.5 or more.
 9. The organic EL light-emitting device according to claim1, wherein the first binder contains high refractive indexnanoparticles.
 10. The organic EL light-emitting device according toclaim 9, wherein the high refractive index nanoparticles are containedin a ratio of 20% by weight or more and 80% by weight or less relativeto a total amount of the first binder.
 11. The organic EL light-emittingdevice according to claim 1, wherein the first light-scattering layerhas adhesiveness.